Telecommunication receivers



March 30, 1965 M. LIGER 3,176,237

TELECOMMUNICAT ION RECEIVERS Filed Nov. 25, 1960 4 Sheets-Sheet 2 4o 4 "m WORK 46 H 2km Fig 3 In ve/17 Nara L ger' f Wwde/wai KW: v m

fforngys March 30, 1965 M. LlGER 3,176,237

TELECOMMUNICATION RECEIVERS Filed Nov. 25, 1960 4 Sheets-Sheet 3 I r 2 Z 22 II OUTPUT NETWORK In ve 117b,

Mare -19 M (la ,9- fimw' Zfforngys United States Patent ()1 3,176,237 TELECOMMUNHZATEON REEEVERS Marc Liger, Draveil, France, assignor to Societe Auonyme dc Telecommunications, Paris, France, a French body corporate Filed Nov. 25, 1960, Ser. No. 7L66 Claims priority, application France, Mar. 2,

aces s Ciaims. (c1. sac-s The present invention concerns :a telecommunication receiver matched to the sources of signals which feed it and occupying any position, intermediate or terminal,

telecommunication link with the signal sources which feed it so that the energy supplied by those sources may be wholly transmitted to the receiver, thus avoiding reflection of a fraction of this energy at the input of the receiver, and interference of the fraction with the incident energy giving rise to amplitude and phase distortion of the received signals which could much reduce the quality of the link. It is also known that the matching of a receiver with the signal sources which feed it does not permit of the noise factor of the receiver being reduced to a minimum, such reduction, or the contrary, being possible only by mismatching the receiver and the signal sources.

The receiver of the present invention is of the type above indicated, and combines the advantage of being matched with the signal sources which feed it with that of having a low noise factor; the receiver according to the invention is characterised by the fact that, with the aim of reducing its noise factor it is made up of several component receivers, preferably mismatched, connected between an output network and an input network to which the signal sources and the matching impedances are joined, these input and output networks being so designed that .at the output of the receiver the signals coming from the said sources and transmitted by the several component receivers, have such amplitude and phase relations that the resultant signal is of maximum amplitude, while the noises coming from the matching impedances and transmitted by the component receivers have, on the contrary, such phase and amplitude relations that the resultant noise is of minimum and preferably zero amplitude.

The several component receivers which make up the receiver of the present invention are constructed according to the band width and middle frequency of the frequency band transmitted by the telecommunication link under consideration; as the case may require they may individually consist of amplifiers, unidirectional conductive elements.

By way of eXample there are described below and shown diagrammatically in the accompanying drawing several constructions of telecommunication receiver according to the invention.

FIG. 1 is a block diagram of a telecommunication link equipped with a receiver according to the invention.

FIG. 2 shows the theoretical diagram of the receiver with which the telecommunication link of FIG. 1 is equipped.

FIG. 3 shows a diagram of a particular construction of the receiver of FIG. 2.

3,l76,237 ?atented Mar. 3t), 1965 "ice.

FIG. 4 is a block diagram of the most general type of telecommunication link which can be equipped with a receiver according to the present invention.

FIG. 5 is a diagram of a particular construction of the telecommunication link of FIG. 4.

The noise at the receiver output results from the noise transmitted by the signal sources, from noise in the receiver itself, and from noise from the matching impedances. In the simple case of a source supplying a signal voltage E, and presenting a noise 6 connected with its internal resistance R, the source feeding a recciver of internal matched resistance R presenting a noise EMF. 6', it is easy to calculate the signal to noise ratio, which for the source is E/c, and for the receiver assumes a value ubstantially equal to E/e /2, that is to say it suffers a reduction of 3 db due to the matching of the receiver to the source; to this reduction of the signal to noise ratio there corresponds a degradation'of the noise factor of the receiver of the same amount 3 db, due mainly to the matching.

The telecommunication receiver of the present invention offers the double advantage of being matched with th signal sources which feed it and of having a noise factor of the least value it is possible to give to known receivers of the same type by refraining from matching them with their signal sources; this result ,is obtained according to the present invention by preventing the noise power of the matching impedances from being transmitted to the receiver output, where it would add to the noise powers coming from the signal sources and from the receiver itself. The diagram of a telecommunication link shown in FIG. 1 suffices to explain the principle of the invention. in this FIGURE 1 is a source of signals, 3 a receiver according to the present invention connected to the signal source by the line 2, and 4 is a matching impedance; the signal source may be represented diagrammatically by a signal 5 of value S in series with a noise EMF. 6 of value B and with a resistance '7 of value R which is the internal resistance; the receiver 3 has been assumed to be a simple six-terminal network, and the terminals being grouped in pairs is shown as a three terminal network, terminal 10 being connected to the line 2, terminal 11 to the matching impedance 4, and terminal 12 to the receiver output terminals to which is connected a resistance R1 which is the load of the receiver and to which it may be matched; the load impedance 4 is shown diagrammatically by a noise S of magnitude B1 in series with a resistance 9 of value R2.

It can be taken that the voltage appearing at the output terminal 12 of receiver 3 results from the combined action on the receiver on the one hand of the signal S and of the noise B coming from the signal source 1 and entering by the terminal 1%), and on the other hand of the noise Bl coming from the matching impedance R2 and entering by the tenninal 11.

As indicated above the general principle of the invention is to reduce to a minimum, and if possible to suppress, the effect of the noise Bl from the matching impedance 4 at the output 12 of the receiver 3, without lowering the signal level at the output, so that the receiver is matched by the impedance 4- without the matching resulting in a higher noise factor; the advantage obtained is what could be expected from matching by an impedance producing no noise, an effect not obtainable prior to this invention.

In the case of a receiver such as 3 in FIGS. 1 and 2, comparable to a six-terminal network, the above-stated general principle of the invention may be translated into conditions governing direction of transmission between the several terminals of the receiver; there are two such conditions,

, produce no noise.

Ist The noise 'enter'in the receiver 3fby its terminal 11 should be transmitted only to the receiver-terminal 10, and

2nd-The signal S andnoise Bwhich enter the re-t ceiverbyits terminal 10, superimposed the one on the other, should be transmitted at least in partto the receiv er output terminal 12, preferably in such fashion that the signal S has maximum amplitude.

The consequence of these two conditions is that, seen from the receiver'terminal 12 the impedance 4 appears to As indicated above there results an improvement in the signal to noise ratio at the output of the receiver, and therefore of the noise factor of the; receiver, by the factor say 3 db; conversely, the same signal to noise ratio can be obtained with the power of the source of signals reduced by a half;

'In its most general form,'shown in block diagr am in FIG. 2; the receiver 3 of the invention is madeup ofan input network 14, an output network-1'5 and an arbitrary,

integral number n of elementary receivers 3p; the input' networkhas n+2 (pairs of) terminals, two of them connected respectively ,to the receiver terminals loand 11,

and the rest numbered 14.1 to 14.11; the output network 15.

has n+1 (pairs of) terminals, one connected to the re ceiver output 12 and the rest numbered 15.1 to 15.12; each of the n elementary receivers 3p has its input and outputs connected respectively to the terminals 14p, p of the input and output networks; the elementary receivers 3p may. be'of anydesired construction suited to the band" width andmid frequency. of the frequency bandtransmittedyby the link in which the receiver 3 is incorporated;

in particularthese elementary receivers canbe amplifiers, rectifiers, diodes, or ingeneral unidirectional transmission integers, so connected as to allowktransmissionto the output network 15 of information received from the input network 14, and tov oppose transmission of information in the opposite sense, 1 a 7 Mathematical analysis of, the conditions governing di rectionof transmission above stated ceiver, 3 in FIG 2 is as follows.

in the caselof there- V rp= I BI B1'E (-b l ll j(flb+ l+ ll p=1 The notation adopted'in the Formulae 3 and 4' is the same as that adopted in the Formulae .1 and 2, b and 18 being respectively the attenuation in nepers and the shift of phase'suifered by the noise B1 between the input ter- 7 minal, 11 of the receiver 3 and the output terminal 14,, of the inputnetwork 14;

Using an obvious notation the Formulae 2 and'4 can be put in the'forrn The conditions governing outuabove areequivalent to" 5' s' o (6) I B=O Compatibility ofv these two equations is the necessary and suificient condition to make possible, design of the direction of transmission set a input and output networks 14' and 15 of the'receiver ac- If S1 be the sum of the signal S and noise. transmitted by the sourceof signals to the inputterminalt 10 of the receiver 3, it-may readily be-shown that'the value of the elementary signal whichv appear-sat the receiver output terminallZ after transmission by the elementary receiver 3p from theinput network 14 to thejoutput network -15 is a San;S Q 'p '"NT D 'WD' /p) and the shift of phase suffered by the input signal S1 between the terminal 10 of the receiver'3 and the terminal 14,, of its input network; a" and 'a are respectively the gain in. nepers and the shift of phase suffered by the signal between the input and outputof the; elementar receiver3 ;and a" and'ix": are res ectivel theatw P p P tenuation in nepers and the shift of phase'of the elementary signal between the terminal15; of the output net work 15 .ofreceiver 3 and" the output terminal 12' of thereceiver.- g a r e The resultant signal appearing at the output terminals 12 is obviously the algebraic sum ofthe several elemen tary signals S' 'which have been transmitted by the sev-; eral elementary receivers 3 so its value is' receiver 3 due to the matching impedance 4 is v where a and a, are respectively the attenuation in neper s cording to the invention, the basic diagram of which is shown in FIG. 2,.so. thatthe. conditions governing direction above mentioned may bevsatisfied and the advantages above indicated maythus be obtained. -In general this, eornpatibility is shown bythe following: it is always possible to give arbitrary valuesto the factors X Y such 'th-at the real'andl imaginarypartsof the'second term of shall not. be simultaneously zero. If these Equation '2' arbitrary values ofthegfa'ctors X Y D are then. substituted inthe-second term of Equation 4', Equation, 6 becomes a complex te a bps p, as

equation the real unknowns ofwhich are the which depend solely upon the input network 14of the receiver 3;" it is generally possible so to choose the characteristics ofxthis in-put network that theresulting valuesvof the terms a u b may be real roots of the complex Equationaa6'; the-elementary receivers 3 and the output network 15 of receiver 3 can thenfbe determinedso that the terms a',,, a

a! all may have such values that, takinginto accouni the value s determined for the terms a b u u the relation (5) maybe. eifectively satisfied; V i M j A particular-example illustrating the compatibility of the relations (5) and-,(6) is as follows; if receiver 3 is so designed that each elementary signal S suffers between the input terminal 10 and the output terminal 12 of the receiver; a total damping and a totalrs'hift of phase a nepers and a in'especive of the order p of the elementary receiver, which transmitted the signal considered, then given b 2"),

Equations 2 and-4' may be put in the following terms g Equation 6/ is replaced by I f a 11 of the receiver" 3 I The resultantnoise at the output ternhinal' 12 of the g the solution of whichfor a fbg, and 3 enables the" determination of the input network 14 :of receiver The simultaneous equations 1 h p+ p "p= 0" amass? can readily be satisfied, for example by adjusting the gains a and the phase shifts of the elementary receivers 3 as a function of the attenuations and phase shifts produced by the input and output networks 14 and 15 respectively of receiver 3 between their input or output terminals or 12, and their terminals connected to elementary receiver 3 In the yet more special case of the input network 14 of receiver 3 being an artificial transmission line the ends of which are connected respectively to the terminals 1% and 11 of receiver 3 while its n tappings 1 are arranged to present infinite output impedance to which the relatively small input impedances of the elementary receivers 3 I connected to them are mis-matched, the supplementary make it possible to put Equation 6 in the form and further, if the input network 14 is purely reactive and so a =0 for any p makes it possible to put Equation 6" in the form I 4 e2inu 1 (6 g ie 0 the solutions of which are k being integral and not a multiple of n. For example in the case of 11:2 elementary receivers.

I k being any integer, from which it follows that the signals issuing from the terminals 14 14 of the input network 14 should be in quadrature.

The design of receiver according to the present invention shown in FIG. 3 of the accompanying drawing corresponds to this last example. This receiver has been so designed that it can be inserted in a telecommunication link transmitting a frequency band the mid frequency of which is near 130 mc./s.; the input network 14 is formed by an artificial delay line made up of three quarter wave elements: 16, of 50 ohms impedance eon nected between the signal input terminal 10 and the terminal 11 to which the matching resistance R of 50 ohms is connected; 17 and 18, each of 75 ohms impedance,

connected respectively between the terminals 10 and 11 on the one hand and terminals 14 and 14 on the other hand, to which latter terminals the inputs of the receivers 3 and 3 are respectively connected. These two receivers are nearly alike in constitution and are formed by amplifiers designed to give maximum gain in the neighbourhood of 130 mc./s.; each amplifier consists essentially of an earthed grid valve; the signal appearing at the terminals 14 14 respectively of the input network 14 is fed to the cathode of the corresponding valve 19, 19' through a high ratio auto-transformer Ztl, 2% to one terminal of which is connected through a gain control potentiometer 21, 21' the source of bias of the valves 1.9, 19'; signals amplified by the valves 19, 1% are collected from their anodes through transformers 22, 22' of even higher ratio than the input transformers 20, 20 (for example a ratio of 3 for transformers 20, 20' and of 12 for transformers 22, 22). The output network 15 consists of a single quarter wave line 23 of 50 ohms impedance the ends of which are connected on the one hand to the terminals 15 15 which are joined to the outputs of the amplifiers 3 3 and on the other hand to the output 12 of the receiver. Since the valves 19, 19' have their grids earthcd their cathode input circuits will be of low impedance, and seen from the inputs 14 and and 14 of the amplifiers 3 3 will seem to be of still lower impedance because of the high ratio transformers 2t), 2%; hence the impedances at the junctions between the quarter wave elements 17, 18 and the artificial line 16 have very high values; as, moreover, these junctions are a quarter wave length apart along the artificial line 16 the disturbances they impart to it practically compensate each other, a d the artificial line seen from its input 10 appears to be exactly matched to the resistance R the value of which is equal to the characteristic impedance of the line, say 50 ohms; the input impedance of the receiver of FIG. 3 is then equal to its matching resistance 4-. On the other hand, the low values of impedance at the ends of the quarter wave elements 17, 1% connected respectively to the inputs of the amplifiers 3 3 are transformed into high impedances by the high ratio transformers 2t 29, and so are mis-matched to the low input impedances of the valves 19, 19', the grids of which are earthed; this mis-matching to the input impedance is known to be favourable to reduction of the noise factor of each elementary amplifier 3 3 It is easy to see that any signal S applied to the receiver input 10 causes two elementary signals 8' and S' to appear at the output 12,, these having traversed respectively the elementary amplifiers 3 and 3 and being, if the amplifier gains are suitably adjusted, substantially in phase and of the same amplitude. The noise B transmitted by the matching impedance 4 to the the input 11 of the receiver, on the contrary, produces at the output 12 two components 3' and B' which differ in phase by twice that is to say are opposite in phase; as, moreover, their amplitudes are nearly alike they compensate one another, and the compensation may be made perfect by suitable adjustment of the gains of the elementary amplifiers 3 3 so at the output 12 there appears no noise component due to the matching impedance 4.

The receiver above described with reference to FIG. 3 has been constructed, and has been found to have a resultant gain of 11 db, and its input impedance, 50 ohms, showed a standing wave ratio of less than 1.2; used as a preamplifier to a standard receiver having a noise factor of 5.5 db, the receiver matched according to the present invention makes possible a composite receiver with a resultant noise factor of about 1.5 db.

The most general form of receiver according to the invention is shown in FIG. 4 and is made up of the following parts: an input network having n+p terminals, terminals 24 to 24,, being connected respectively to sources of signals or of noise or of both S to S through impedances Z to Z assumed to be free of noises; imped ances Zj (i being any integer between 1 and 1' included) associated with signal sources 8, and representing the internal impedances of those sources; impedances 2 associated with noise sources 8, and representing matching impedances each producing noise corresponding to the associated source; terminals 14 to 14,, of the input network connected respectively to the inputs of component receivers 3, which must satisfy the one condition of transmitting information unidirectionally from their inputs totheir outputs; and

anfoutput network having terminals 1'5 "to,15,, connectedto the outputs of the n component receivers, and having also-m outputs to a 25 to lwhichla're respectively connected impedancesZ some of which may represent receiving apparatus infthe; telecommunication network under consideration, and 7 others matching impedances of the output network 7 15. The principaltcharacteristic ofthis receiver-sis that theinputand output networks are so'designed that at all outputs 25,, of the receiver which areconnectedi'to receiving impedances Z' signalslcoming from sources '8 and transmitted by diiierent component receivers 3 are so related in phaseand'amplitude that the resultant signal is of maximum amplitude, while thenoises comingfrom matching impedance Z; and also trar ismittedtby the component receiver s 3 are, on the contrary, so related in phase. and amplitude at outputsof the receiver that the resultant noise is of minimum and preferably'zero amplitude. This characteristic can be expressed mathematically, set-ting out from' the expression for the ;resultant signal S which appears at the terminals of'the receiving impedance Z' namely, I t a t t I i=1 V i S k=E h E I where E is the electromotive 'force' of the sourceS of signal or noise,

11 is a coefiicient depending on the input network 12,

the output network 15, the component receivers 3 and the frequency of the signals transmitted. a

' In this equation: control'of' direction inthe receiver from its inputs 24 24 24 (1, mpn being'ditferent integers betweenl and p included), for example, toits.

27 by the two impedances 26, 26', and that the noises emitted by each matching impedance and transmitted by the several component receivers 3 to 3 have, at the output 25 such amplitudes" and phasesthat they Wholly compensate each other; on the other hand, at thev output 25 these resultant noises from the matching impedances arev of such amplitudes and phases that they add and do not-cancel out; so'all the noise produced by the matching impedances 26, 26 is transmitted by thereceiver of FIG. 5 to the impedance 30" alone, the impedance, 30, receiving none of it; also, the component signals resulting from the transmission of the signal S produced by source 27 through the three'cornponent receivers 3 to 3 1 are in phase at the outputterrninal .25 where their amplitudes add together, while atv terminal ,25 they are in opposing phases and of suchamplitudes that they cancel out; so the signal'emitted by the source 27 is transmitted only to impedance 31), not to impedance 30.

I Iris possible to conneetin cascade a plurality of receivers matched according to the present invention, having the same numbers of input terminals and output terminals respectively, the input terminals of one receiver it is employed;

output terminals 25,, is "represented by the factthat. all

the parameters 'h are zero except h h h t'in' the example considered. If these conditions governing direc tion are satisfied the signals emitted by the sources S 5 ,8 are transmitted to the output 25;; of the receiver atan amplitude that is not zero,'while, on the contrary,

none of.theno ise produced by vthe matching impedances 2 connected to'the receiver terminals otherthan 24 2%,, 24, is transmitted to the output terminal 25;. The particular case shown in FIG. 5 comprises a sing] signal source'27 of electromotive force S andof internal resistance R5, and two identical'matching impedances 26, 26', each of which may be represented by 'asource of noise of electromotive force B in series with a resistance of twice the magnitude ofthe internal resistance'of the j signal source 27, SayR 1 The input network 14 is made up of two quarter wave line elements 28, 2 8'; 'of'thephase shifts are respectively a' a' being connected to the output terminals of the preceding receivergsuch an arrangement can greatly'improve the noise factor of the whole telecommunication link in which .I claim n V 1 a I a 1. A telecommunication receiver, comprisingan input phase-shifting network having input terminals connected to at least one source of signals and to at least one matching impedance for said source'of signals, and a'plurality of output terminals, an output phase-shifting network having a plurality of input terminals and at least one out-. put load terminal, and a plurality of unidirectional transmission devices It in number, having respective inputs and outputs, between which the transmission factorsrand a' ands d ot' impedance transforming means for connecting therethrough the inputs of said transmission device's respectively to output terminals of said input network t at Whichthe successive transmission attenuations and same characteristic impedance R grthe. junction of 28 and v "28is connected to the input terminal 24, of the input network 114 to which the signal source 2,7 is connected, as welltas to the output terminal 14 of theinput network l4; the remaining ends of 28, and 128" are respectively connected to the input terminals 24 24 0f the input network to which the matching. impedances 26, 26'

are joined, as well as to the, output terminalsl l 14 0f network 14; the three component amplifiers 3 to 3 the inputs of which are connected respectively, to the outputs 14 1-to-14 of the input network, have gains GLZG and G respectively; their outputs are; connected to the -'inputs.'1 5 to 15 of the output network 15 whichteonsistsj of asingle quarter wave line element 28 of, characteristic,

impedance 2 one end of which is joined; to the input terminal 15 of'the output network, 15,and,also to its outputterminal 25 while its;other end is connected both to'the two input terminals 15 and15 and to' th'e output terminal .25 two matching impedances ,30 and- 30 are fconneoted to theoutput terminals 25 and 25 of the output network 15 of a value equal to the ,charac! teristic impedance Z5 of the quarter wave element 29.

phase shifts measured from the; input'terminal thereof connected to said source of signals, are respectively a a' a and m 01 A a said attenuations and phase vshifts having substantially the relationship where j=' I, said: transforming-means being adapted for impedance-mismatching the inputs of, said transmission devices with'the said output terminals of the input network to which the said last inputs are connected-thereconstantand'respectively oer-M Oz -0K through, and the outputs of said transmission devices being connected'toinput terminals of said output network from. which successively the transmission attenuations and phase shifts measured at the saidfoutput load terminal thereof are equal to the differences between an arbitrary 2. A telecommunication receiver comprisingan input delay line connected at one end, to, a source. of signals 7 and at the other'end to ja -matching impedance for said 1 source of signals, an output delay line connected at one 7 .end to a loadandat the other end to a terminating impedanceyeachof said delay lines;consisting inv (n-l) tandem-connected, attenuation-free,"sections each having a same phase shift equal, to 18Q xk/n where'k is any integer-not being a' multi'ple of n, a plurality of amplifiers n innumbenall having substantially a same phase shift from input, to output. thereof, impedance transfo'rming means for connecting therethrough the inputs of said amplifiers respectively to the section junction points on said input line, said transforming means being adapted for impedance-mismatching the inputs of said amplifiers with the said junction points on the input line, and the output of each of said amplifiers being connected to the section junction point on said output line at which the phase shift measured from the said other end of the output line is substantially equal to the phase shift measured between the said one end of the input line and the junction point thereon to which the input of the same amplifier is connected through said transforming means.

3. A telecommunication receiver for receiving a band of frequencies, comprising an input delay line connected at one end to a source of signals and at the other end to a matching impedance for said source of signals, an output delay line connected at one end to a load and at the other end to a terminating impedance, each of said delay lines consisting in one quarter wave section for the midfrequency of the band to be received, first and second substantially identical amplifiers, having very low input impedances, the outputs of said first and second amplifiers being connected respectively to the said other end and the said one end of the output line, a first and second 10 other quarter wave line sections connected at one end respectively to the said one end and the said other end of the input line, and first and second high ratio transformers inserted respectively between the other ends of said first and second other line sections and the inputs of said first and second amplifiers.

References Cited by the Examiner UNITED STATES PATENTS 1,949,217 2/34 Nakken 330-124 X 2,043,587 6/36 Macalpine 330-124 X 2,263,376 11/41 Blumlein et a1. 330-54 2,545,871 3/51 Bell 333-29 X 2,552,160 5/51 Espley 250-54 X 2,790,956 4/57 Ketchledge 333-29 X 2,921,134 1/60 Greenspan et al 333-29 X 2,922,965 1/ 60 Harrison 333-29 X ROY LAKE, Primary Examiner.

L. MILLER ANDRUS, NATHAN KAUFMAN,

Examiners. 

1. A TELECOMMUNICATION RECEIVER, COMPRISING AN INPUT PHASE-SHIFTING NETWORK HAVING INPUT TERMINALS CONNECTED TO AT LEAST ONE SOURCE OF SIGNALS AND TO AT LEAST ONE MATCHING IMPEDANCE FOR SAID SOURCE SIGNALS, AND A PLURALITY OF OUTPUT TERMINALS, AN OUTPUT PHASE-SHIFTING NETWORK HAVING A PLURALITY OF INPUTS TERMINALS AND AT LEAST ONE OUTPUT LOAD TERMINAL, AND A PLURALITY OF UNIDIRECTIONAL TRANSMISSION DEVICES N IN NUMBER, HAVING RESPECTIVE INPUTS AND OUTPUTS, BETWEEN WHICH THE TRANSMISSION FACTORS AND PHASE SHIFTS ARE RESPECTIVELY A''1, A''2 ... A''N'' AND A''1, A''2 ... A''N, IMPEDANCE TRANSFORMING MEANS FOR CONNECTING THERETHROUGH THE INPUTS OF SAID TRANSMISSION DEVICES RESPECTIVELY TO OUTPUT TERMINALS OF SAID INPUT NETWORK AT WHICH THE SUCCESSIVE TRANSMISSION ATTENUATIONS AND PHASE SHIFTS MEASURED FROM THE INPUT TERMINAL THEREOF CONNECTED TO SAID SOURCE OF SIGNALS, ARE RESPECTIVELY A1, A2 ... AN AND A1, A2 ... AN, SAID ATTENUATIONS AND PHASE SHIFTS HAVING SUBSTANTIALLY THE RELATIONSHIP 